POST-INFLATIONARY COSMOLOGICAL MODEL-BASED ON THE 7-DIMENSIONAL SUPERGRAVITY

We study classical solutions of the bosonic sector of seven-dimensiona l supergravity theory. This study is three-fold: first, we look for po wer law solutions in a space which is the Cartesian product of a four- dimensional Robertson-Walker metric and a compact internal space; next , for the same geometric configuration, we sketch the phase diagram of all possible stable solutions; finally, we consider the evolution of scalar fluctuations on the background of the exact solutions found her e. We observe that in spite of the presence of a potential term and a nontrivial coupling of three scalar fields, no inflationary scenario c an emerge from such theory, and that all stable solutions display a bi g-bang type singularity. We conclude that the supersymmetric theories are well suited to describe the post-inflationary behavior of the Univ erse emerging from the inflationary phase before it enters the pure ra diation stage.